زينب

• Process selection

  1. List design requirements

  2. Plot requirements on process charts

  3. Identify search areas

  4. Processes that overlap search areas are candidates

  5. If no one process meets all requirements, stack processes
• Design requirements

  Material, shape, size, minimum section, precision, and finish
• Sequence of process selection

  1. List design requirements

  2. Plot requirements on process charts

  3. Identify search areas

  4. Processes that overlap search areas are candidates

  5. If no one process meets all requirements, stack processes
• The process selection charts inputs are design requirements; the output is a ranked short-list of processes capable of meeting design requirements
• Stacking processes


  • Casting followed by machining (to meet the tolerance specification on one surface, for instance); or powder methods followed by grinding
• The sequence of process selection using process selection charts is the input of design requirements, and the output is a ranked short-list of processes capable of meeting design requirements
• Candidates


  Processes that overlap the search areas and are capable of making the component to its design specification
• If no one process meets all the design requirements, then processes have to be "stacked"
• Forming


  The process of shaping a material into a desired form
• Fan for vacuum cleaners

  • Designed to be cheap, quiet, and efficient
  • The key to minimizing process costs is to form the fan to its final shape in a single operation (net-shape forming)
  • Leaving only the central hub to be machined to fit the shaft

  
• The selection of a single process that can meet the specifications on precision and tolerance, avoiding the need for machining or finishing of the disk or blades
• Fan

  • Blades made of nylon, require low roughness and a certain precision, produced in large numbers for use in electric vacuum cleaners
• Design requirements for the fan

  • Material (nylon)
  • Radius (60mm)
  • Number of blades (20)
  • Blade thickness (4mm)
  • Weight (0.1-0.2kg)
  • Shape (3D solid)
  • Precision (0.5mm)
  • Surface roughness (1mm)
  • Production run (10,000)

  
• The design requirements for the fan are summarized in Table 1

  
• The next step is to identify the processes that can meet these design requirements
• Material choice for the fan

  Nylon (using material selection charts)
• Pumping rate of a fan


  Determined by its radius and rate of revolution
• The designer calculates the need for a fan of radius 60mm, with 20 profiled blades of average thickness 4 mm

  
• Volume of material in the fan

  Roughly, a weight in the range 0.1 - 0.2 kg
• Fan


  • Complex shape, though its high symmetry simplifies it somewhat
  • Classified as 3D solid
• Precision (tolerances)

  0.5mm
• Surface roughness


  1 mm
• Production run of 10,000 fans
• The design requirements are summarized in Table 1
• Processes that can meet the design requirements

  1. Screening on mass and section thickness

  2. Constraints on tolerance and roughness

  3. Planned batch size of 10,000

  
• The process-shape compatibility matrix of the three case studies is a helpful tool in narrowing the choice, suggesting alternatives, and providing a background against which a final selection can be made
• Weight of the fan

  0.1 - 0.2 kg
• Section thickness of the fan

  4 mm
• Tolerance (Precision)

  0.5mm
• Fan production quantity = 10,000 fans
• Surface Roughness


  Less than 1 mm
• The table shows the candidate processes that were screened using the process selection charts, where some processes were eliminated for not meeting all the constraints, leaving only the processes that met all the requirements
• The final process selection depends on the process that can produce the fan at the lowest cost, where the processes are ranked from lowest to highest cost

  
• A pressure vessel is required for a hot-isostatic press or HIP
• Pressure vessels

  • Designed to yield or leak before they break
  • Small pressure vessels are usually designed to allow general yield at a pressure still too low to cause any crack the vessel may contain to propagate
• Large pressure vessels are always made of steel
• A model steam engine is made of copper, even though it is more expensive, because of its greater resistance to corrosion
• Corrosion rates do not scale with size, so a 0.1mm loss through corrosion is not serious in a 10mm thick pressure vessel, but becomes a concern in a 1mm thick vessel
• Pressure vessels still occasionally fail
• Small pressure vessels

  • Designed to allow general yield at a pressure still too low to cause any crack the vessel may contain to propagate
  • Distortion caused by yielding is easy to detect and the pressure can be released safely